Exam 3 Study Guide Orenda Johnson PSB2000 Internal Regulation Homeostasis biological processes that keep body variables within a fixed range Allostasis the adaptive way in which the body changes its set point in response to changes in life or the environment Set point a single value that the body works to maintain o Ex levels of water oxygen glucose etc Thermoregulation o Why do we maintain our body temp so close to the high end of safe Muscle activity benefits from being as warm as possible and ready for vigorous activity o Hypothalamus role o Fevers Gets temperature info from thermoreceptors in the skin Cools the body through vasodilation and sweating Heats the body through shivering increasing metabolic rate and decreasing blood flow to the skin Parts involved in heating and cooling Pre optic area anterior hypothalamus cools you off Posterior hypothalamus warms you up When you get sick bacteria and viruses trigger the release of leukocytes which release small proteins called cytokines They not only attack intruders but they also stimulate the vagus nerve which stimulates the hypothalamus which increases the set point body temperature This heat is good because some bacteria grow less quickly and it enhances the activity of the immune system At the beginning of a fever you feel cold Your body does this in order to prompt you to do things that raise body temperature like wearing warm clothes or drinking hot liquids By making your normal body temperature feel chilly instead of comfortable it s pushing you to behave in ways that raise your temperature a little higher Once the bacteria are killed and our immune reactions stop our internal thermostat abruptly drops back to normal This causes our body to do what it s supposed to do when we re too warm which is sweat A LOT This is called breaking a fever High solute concentration outside of a cell causes a loss of water due to osmosis Your body wants an even concentration Thirst o Osmotic thirst Hunger o What are signals to eat o Hypovolemic thirst of a solute throughout your body so when you eat salty food your body takes water out of your extracellular fluid to even it out Detected by neurons in circumventricular organs Makes you thirsty for pure water Associated with a low volume of body fluids due to sweating vomiting or especially bleeding Defected by neurons that monitor blood pressure and the subfornical organ Makes you thirsty for slightly salty water Social and environmental cues The desire to taste Peripheral hormones such as Ghrelin Metabolic signals such as a drop in glucose or lipids o Relationship between insulin and glucose Low levels of insulin and glucose are hunger signals and make you want to eat High levels however are satiety signals and tell your body that you don t need any more food Insulin also helps glucose enter cells for use or storage High levels increase physical and immune system activity but o Leptin don t always decrease hunger Low levels increase hunger Produced by fat cells o How the hypothalamus regulates hunger The first hypothalamic region to receive hunger and satiety signals is the arcuate nucleus Two kinds of neurons are present one being hunger motive and one being satiety motive They each have many input factors that cause them to be activated The second region is the paraventricular nucleus which inhibits the lateral hypothalamus The third region is the lateral hypothalamus which promotes feeding behavior There s a flow chart illustration on slide 25 of the Internal Regulation PowerPoint if this doesn t make sense here Detects hunger which in turn signals the brainstem and cortex to enhance taste This is the cortex for general arousal and food seeking Damage to this causes many stages of an eating disorder depicted in the illustration below found on slide 28 o Lateral hypothalamus o Periventricular nucleus Satiety promoting Damage to this causes you to eat a normal number of meals but they are very large each time o Ventromedial hypothalamus Satiety promoting as well Damage to this and its surrounding area causes you to eat normal sized meals but unusually frequent Organizing and Activating Effects of Hormones 3 classes of sex steroid hormones o Androgens Testosterone DHT o Estrogens Estradiol o Progestins Progesterone o Sex hormones are very similar and even share a common pathway of synthesis So testosterone can either exert its effects by working at testosterone receptors or be converted to estradiol or DHT and work at those receptors instead Differences between organizational and activational effects of hormones o Organizing effects Occur mostly during sensitive periods in development before birth in humans Effects are generally permanent Determine whether the brain the body will develop male or female characteristics o Activating effects Occur at any time in life when a hormone temporarily activates a response physiological or behavioral Effects last only as long as the hormone is present This includes menstrual cycles in women and sexual excitement in men Males and females differ in their X and Y sex chromosomes o On the male Y chromosome there is an area called the Sex Determining Region of the Y Chromosome SRY This gene signals male development o The default development pattern is female because without the SRY gene the fetus will develop female characteristics Males need the hormone signal to override the female plan A male can be feminized or demasculinized by removing androgens or blocking androgen receptors So things like castration a lack of androgen receptors or drugs that block the effects of testosterone can be feminizing or demasculinizing if they occur during a critical period of development A female without estrogen during that same critical period will develop normal sexual anatomy but present abnormal sexual behavior Hormones affect sexual behavior in rats as well Pattern of testosterone levels change in both males and females o Males fluctuate up and down throughout the day o Females consistently low throughout most of the menstrual cycle but begin to increase around day 5 and peak at day 14 during ovulation Menstrual cycle o Hormones involved include estrogen estradiol progesterone from the ovaries and luteinizing hormone LH follicle stimulating hormone FSH from the anterior pituitary o Hormone cycles o When a woman is periovulatory her hormone levels change Estrogen is high Progesterone is beginning to rise Testosterone is as high as it gets in a female Because of
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